Ion implantation is commonly used for doping a semiconductor material at precisely controlled depths and dopant concentrations. An ion implanter generally includes an ion source to generate an ion beam, ion beam transport optics for accelerating the ion beam, and a process chamber where the ion implantation on a semiconductor wafer occurs. The ions are mostly positively charged.
An ion beam containing dopants is generated in an ion beam source chamber. Thermionic electrons are first generated from a metal such as tungsten filament which is heated by a current source. The filament is also negative biased. Thermionic electrons are generally accelerated by the biased potential, and collide with molecules of dopant precursors to generate plasma comprising dopant ions.
During ion implantation, the charged ion beam strikes the semiconductor wafers in the process chamber, resulting in a doped semiconductor wafer when the dopant ions diffuse into the wafer.
Meanwhile, the size of semiconductor wafers has gradually increased to improve throughput and reduce cost per die. For example, in the transition from 300 mm to 450 mm wafer size, the wafer area increases by 125%. The within wafer uniformity (WiWU) becomes more difficult to maintain in the more-than-double-sized wafer.